Well stated. Application is important to making decisions on valve angles. NASCAR are pretty much all using 50° to 55° seats. High lift and RPM dictate those angles. Street engines get minimal benefit from those angles. With max lift at or under 0.600" the seat curtain is the controlling factor up to about 0.350" to 0.400". Back cut intake valves and 40° exhaust seats provide a benefit to these lower RPM engines. When installing larger valves, shrouding is a definate concern considering the cylinder wall and head gasket sealing surface limit how far clearancing can be pushed. The combustion chamber wall by the intake valve seat can be relieved to aid low lift flow during the important scavenge cycle during overlap. Caution on cam dwell and overlap must be exercised to not blow too much intake charge out the exhaust at lower RPM street driving conditions.